The DPP has failed in a bid to narrow the scope of the inquiry into David Harold Eastman's conviction for the murder of Colin Winchester.

Acting Justice Kevin Duggan's decision at this morning's Supreme Court directions hearing paves way for the broad-ranging inquiry to proceed next year.

The costly probe has yet more hurdles to jump.

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Questions had surrounded funding for the inquiry, with the Legal Aid Commission earlier warning Eastman's representation couldn't be paid for in their current budget. But a spokeswoman for newly reappointed Attorney-General Simon Corbell has confirmed the government will give the commission extra cash to represent the convicted murderer.

However, Eastman's counsel, Terry O'Donnell, faces the potentially thorny problem of becoming a witness in his client's case.

Assistant Australian Federal Police Commissioner Colin Winchester was gunned down in the driveway of his neighbour's home in Deakin in January 1989.

A jury convicted Eastman of the slaying in 1995.

He has served 17 years of a life sentence, but has always maintained his innocence.

Earlier this year Justice Shane Marshall ordered a new inquiry into the soundness of the conviction.

The judge was satisfied there was a "fresh doubt or question" about Eastman's guilt.

He ordered the inquiry based on 19 wide-ranging grounds proposed by Eastman's lawyers.

They canvas mental health issues, forensic evidence and the conduct of the prosecution and investigating police.

Director of Public Prosecutions Jon White applied to limit the scope of the inquiry to just one ground, arguing everything else had already been fought out at earlier hearings.

The sole ground was the emergence of a witness who claimed he borrowed Eastman's car to go rabbit shooting in the 1980s and put a rifle in the boot.

Eastman's lawyers argue that could explain the presence of gunshot residue in the boot.

Counsel assisting the inquiry, Liesl Chapman, SC, this morning said the director's application came too late in proceedings.

And Justice Duggan refused to narrow the scope of the probe, ruling he had no power to do so and the time for such a move had passed.

Mr O'Donnell this morning also raised the prospect he might be required to give evidence in relation to the rabbit shooting issue.

The barrister told the court he expected his evidence to be non-contentious and limited to the timing of the discovery.

But Mr White said it was a "troubling" issue, and Justice Duggan said it was a matter for Mr O'Donnell's instructing solicitors – the Legal Aid Commission – to sort out.

Eastman's lawyers have also flagged an intention to seek more documents alluded to in a cache of reports released to The Canberra Times under freedom of information laws.

This week The Canberra Times revealed a major scientific witness, Bob Barnes, had been sacked from the Victoria Forensic Science Centre in 1993 after concerns were raised about his evidence in a number of cases.

That information was not put before the Eastman jury.

The judge said the inquiry proper could not get underway until the money question was settled, but that he hoped to begin in March at the latest.